A worrying number of clinics that directly advertise expensive, unproven stem-cell therapies to patients with serious eye diseases, often with devastating results, are operating across the US, a new study warns.

Although there are no approved stem-cell therapies to treat eye conditions in the US, when the authors of the study conducted a systematic web search, they found 40 companies with 76 clinics that advertised the procedures.

Desperate to save their vision, patients with conditions like macular degeneration and optic neuritis may respond to these advertisements, often at tremendous personal cost, the researchers wrote in Ophthalmology.

“Patients have paid anywhere from $5000 to upwards of $50,000 per treatment,” said co-author Dr Rajinder Nirwan, from the Flaum Eye Institute at the University of Rochester Medical Center, New York.